The present invention relates generally to semiconductor process equipment. More particularly, the present invention relates to a gas jet assembly suitable for use in a semiconductor processing reactor and a method of using the gas jet assembly.
Semiconductor processing typically involved the formation of one or more layers on a semiconductor substrate. For example, silicon epitaxy, sometimes called epi, was a process in which one or more layers of single-crystal (monocrystalline) silicon were deposited on a monocrystalline silicon wafer.
To form a layer on a substrate, a process gas, typically a reactive gas, was introduced into a reactor containing the substrate. The process gas reacted to form the layer on the substrate.
As the art moves towards reduced feature size integrated circuits, it has become increasingly important that the deposited layer has a uniform thickness. One primary parameter, which affected the thickness uniformity of the deposited layer, was the flow characteristics of the process gas into and through the reactor. These flow characteristics were controlled to a large extent by the gas injectors through which the process gas was introduced into the reactor.
To obtain the desired thickness uniformity, the gas injectors were calibrated. Calibration was typically an iterative manual process in which a first layer was deposited on a first test substrate, the thickness uniformity of the first layer was measured, and the gas injectors were manually adjusted in an attempt to improve the thickness uniformity. A second layer was then deposited on a second test substrate, the thickness uniformity of the second layer was measured, and the gas injectors were again manually adjusted. This trial and error manual procedure was repeated until the desired thickness uniformity was obtained.
To allow the gas injectors to be calibrated in the above manner, the gas injectors had to be readily and repeatably adjustable. Finn et al., U.S. Pat. No. 5,843,234, which is herein incorporated by reference in its entirety, teaches a gas jet assembly in which the direction of a nozzle of the assembly was controlled by a positioning device. By manually adjusting micrometer knobs of the positioning device, the direction of the nozzle, and therefore the direction in which process gas was introduced into the reactor, was controlled.
To adjust the micrometer knobs of the positioning device, the person who operated the reactor (the operator) had to physically go to the positioning device and turn the micrometer knobs by hand. This required the operator to leave the reactor controls temporarily unattended, which was undesirable. Further, turning the micrometer knobs by hand was relatively labor intensive and carried an inherent chance of operator error in micrometer knob adjustment.
The gas jet assembly of Finn et al. pivoted the nozzle relative to the reactor. Although allowing for pivoting of the nozzle, the gas jet assembly did not allow the nozzle to be moved in and out of the reactor. However, it is desirable to not only be able to control the direction of the process gas into the reactor, but also to be able to control the location within the reactor at which the process gas is introduced.
It was also important to avoid contamination of the reactor to allow high purity layers to be deposited. One potential source of contamination was the metal, e.g., stainless-steel, of the nozzle. In particular, the metal nozzle was often etched during processing, and this etched metal contaminated the deposited layer. To avoid etching of the metal nozzle, shielding was used in an attempt to isolate the metal nozzle from the activated process gas in the reactor. Although the shielding was relatively effective, etching of the metal nozzle was observed depending upon the particular process performed.
In accordance with the present invention, a system in which a single computer controls both a reactor and a gas jet assembly is presented. In one embodiment, the gas jet assembly is mounted to the reactor such that a gas injector extends vertically up and into the reactor, i.e., the longitudinal axis of the gas injector is vertical. The gas injector includes a bent tip which extends at an angle away from the longitudinal axis of the gas injector.
Recall that in the prior art, the nozzle of the gas jet assembly was pivotable relative to the reactor. However, the gas jet assembly did not allow the nozzle to be moved in and out of the reactor. This limited the ability to control the location within the reactor at which the process gas was introduced, and hence, limited the ability to control the process.
In contrast, the gas injector is readily moved in and out of the reactor, and rotated, by the gas jet assembly. Accordingly, greater process control is obtained using the gas jet assembly in accordance with the present invention than in the prior art
Further, in one embodiment, the operation of the gas jet assembly, and thus the angular and longitudinal positions of the gas injector, is based on information supplied by an operator. Advantageously, the gas injector is moved automatically without manual intervention.
Recall that in the prior art, the operator physically had to go to the positioning device and turn micrometer knobs by hand to adjust the nozzle of the gas jet assembly. This required the operator to leave the reactor controls temporarily unattended, which was undesirable. Further, turning the micrometer knobs by hand was relatively labor intensive and carried an inherent chance of operator error in micrometer knob adjustment.
In contrast, use of the gas jet assembly in accordance with the present invention eliminates the prior art requirement of manually adjusting micrometer knobs. As a result, labor is saved and operator error is reduced. This, and turn, results in a lower overall operating cost of the reactor. Further, the gas jet assembly precisely controls the longitudinal and angular positions of the gas injector. Accordingly, the direction and position at which process gas is introduced into the reactor is precisely controlled.
In accordance with another embodiment of the present invention, a method of controlling a gas injector in a reactor with a gas jet assembly includes selecting a first gas injector position for a first process operation, e.g., for an etch cleaning of substrates in the reactor. The gas injector is moved by the gas jet assembly automatically to the first gas injector position without manual intervention. The first process operation is performed.
A determination is made that a second process operation is still to be performed. For example, the second process operation is a layer deposition on the substrates. A new second gas injector position for the second process operation is selected. The gas injector is moved by the gas jet assembly automatically to the second gas injector position without manual intervention. The second process operation is performed.
Thus, in accordance with the present invention, the gas injector is moved to a gas injector position which provides the best results for each process operation. In this manner, each process operation is optimized. This is in contrast to the prior art where a single gas injector position was used for all process operations, and the single gas injector position was less than ideal depending upon the particular process operation.
In another embodiment, a first batch of substrates is processed. A determination is made that a second batch of substrates is still to be processed. The characteristics of the processed substrates from the first batch are measured, for example, the thickness uniformity of a layer deposited on at least one of the processed substrates is measured. Based on these measured characteristics, a new second gas injector position for the second batch of substrates is selected. The gas injector is moved by the gas jet assembly automatically to the second gas injector position without manual intervention. The second batch of substrates is processed.
Advantageously, substrate characteristics from a previous batch are used to optimize the gas injector position for the next batch. In this manner, deviations in process conditions from batch to batch are automatically compensated for resulting in consistent substrate processing from batch to batch.
In another embodiment, a process operation is initiated and a gas injector is moved during performance of the process operation by a gas jet assembly. For example, the gas injector is rotated and/or moved in the longitudinal direction.
In accordance with this embodiment, the operational conditions in the reactor are monitored during the process operation. The optimum gas injector position is determined based on the monitored operational conditions. The gas jet assembly moves the gas injector to the optimum gas injector position. The operational conditions of the reactor are continuously monitored, and the gas injector is continuously moved to the optimum gas injector position during the entire process operation.
Thus, in accordance with the present invention, the gas injector position is responsive to the operational conditions existing in the reactor at all times. In this manner, instantaneous deviations in operational conditions are automatically compensated for resulting in the most optimum processing of the substrates.
In one embodiment, a gas jet assembly includes a gas injector having a longitudinal axis, a first motor coupled to the gas injector and a second motor coupled to the gas injector. The first motor controls a position of the gas injector along the longitudinal axis of the gas injector. The second motor controls the angular position of the gas injector around the longitudinal axis of the gas injector.
In one particular embodiment, the gas jet assembly includes a shaft support, a hollow shaft extending concentrically through the shaft support, and a slider movably supported on the shaft support. The first end of the shaft is located within the slider and a gas injector is coupled to the slider. During use, process gas is supplied to the shaft. The process gas flows from the shaft through the slider and into the gas injector.
To use the gas jet assembly, a seal is formed between the slider and the shaft, e.g., with an O-ring. As set forth above, the gas injector is coupled to the slider. The gas injector is moved by moving the slider relative to the shaft.
In other embodiments, a gas jet assembly includes a pivotable gas injector. By having the ability to pivot the gas injector, greater control of process gas introduction into the reactor is obtained. Further, the gas injector is formed of a nonmetallic material such as quartz, graphite or ceramic. By forming the gas injector of nonmetallic materials, contamination from the metal of nozzles of the prior art is avoided.
In the prior art, the gas jet assembly imparted significant stress on the gas nozzle and so the gas nozzle was formed of metal to avoid cracking and failure of the gas nozzle. Recall that shielding was used in an attempt to avoid etching of the metal nozzle and thus to avoid metal contamination of the deposited layer. However, etching of the metal nozzle was still observed depending upon the particular process performed.
Advantageously, the gas injector is pivotable and thus provides flexibility in controlling process gas flow characteristics into and through the reactor. Yet, the gas injector is formed of a nonmetallic material thus avoiding metal contamination of the prior art. In addition, by forming the gas injector of an infrared transparent material as those of skill in the art will understand, e.g., of quartz, heating of the gas injector is minimized thus minimizing deposit formation on the gas injector.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.